Batch scripts
=============

As seen earlier (:ref:`job_script`), the typical way of creating a job is to write a job submission script. Which is a shell script (e.g. a Bash script) whose **first comments**, if they are prefixed with ``#SBATCH``, are interpreted by :term:`Slurm` as parameters describing resource requests and submissions options [#sbatch]_. 

* See ``sbatch`` manual page [#sbatch]_ for all available directives,
* See our `repository of examples scripts <https://github.com/ltaulell/submission_scripts>`_.

For instance, the following script would request one task with one :term:`CPU` for 10 minutes (default allowed time), along with 2 GiB of :term:`RAM` memory, in the default partition (E5):

.. code-block:: bash

    #!/bin/bash
    #
    #SBATCH --job-name=test
    #SBATCH --ntasks=1
    #SBATCH --cpus-per-task=1
    #SBATCH --mem-per-cpu=2G

    hostname -s
    sleep 60s

When started, this job will launch the command ``hostname`` on the node on which the requested :term:`CPU` was allocated. Then, a second job step will run the ``sleep`` command.

You can create this job submission script on any login nodes (See :doc:`login_nodes`) using a text editor such as nano or vim (See :doc:`../environment_and_tools/editors`), and save it as ``submit.sh``.

.. TIP:: **You can submit jobs from any login node to any partition. Login nodes are only segregated for build (CPU µarch) and scratch access.**

.. caution::

    ``#SBATCH`` **directives must be at the top of the script**, with no empty line(s) in between.

    :term:`Slurm` will ignore all ``#SBATCH`` directives after the first *non-comment line* (that is, the first line in the script that doesn't start with a ``#`` character). Always put your ``#SBATCH`` parameters at the top of your batch script. For example :

    .. code-block:: bash

        #!/bin/bash
        #
        #SBATCH --job-name=big_job

        #SBATCH --mem=16G
        #SBATCH --time=0-00:15:00
        #SBATCH --partition=E5

    will cause *--mem* and all following ``#SBATCH`` directives to be ignored and the job to be submitted with the default parameters.

    **Spaces in parameters will cause** ``#SBATCH`` **directives to be ignored**

    Slurm will ignore all ``#SBATCH`` directives after the first white space. For instance directives like those:

    .. code-block:: bash

        #SBATCH --job-name=big job

    .. code-block:: bash

        #SBATCH --mem=16 G

    .. code-block:: bash

        #SBATCH --partition = Cascade

    will cause all following ``#SBATCH`` directives to be ignored and the job to be submitted with the default parameters.


We provide a `repository of examples scripts <https://github.com/ltaulell/submission_scripts>`_, with various conditions, that may help you write your own.



.. [#sbatch] You can get the complete list of parameters by referring to the ``sbatch`` manual page (``man sbatch``).